U.S. patent number 4,977,297 [Application Number 07/509,407] was granted by the patent office on 1990-12-11 for amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole.
This patent grant is currently assigned to E. I. du Pont de Nemours and Company. Invention is credited to Edward N. Squire.
United States Patent |
4,977,297 |
Squire |
December 11, 1990 |
Amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole
Abstract
Articles made from amorphous dipolymers of
perfluoro-2,2-dimethyl-1,3-dioxole with tetrafluoroethylene having
high glass transition temperatures of 140.degree. C. or higher, low
indices of refraction, and good physical properties, and low
dielectric constants, include, among others, substrates for circuit
boards, composites, sheets and films, optical lenses, and
electronic current carrying devices.
Inventors: |
Squire; Edward N. (Spring Hill,
FL) |
Assignee: |
E. I. du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
27404302 |
Appl.
No.: |
07/509,407 |
Filed: |
April 9, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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458012 |
Dec 28, 1989 |
4948851 |
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148579 |
Jan 26, 1988 |
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904095 |
Sep 4, 1986 |
4754009 |
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723649 |
Apr 16, 1985 |
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591486 |
Mar 20, 1984 |
4530569 |
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294789 |
Aug 20, 1981 |
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Current U.S.
Class: |
174/258; 361/748;
361/751; 428/901 |
Current CPC
Class: |
C08F
234/02 (20130101); H05K 1/034 (20130101); H05K
3/285 (20130101); Y10S 428/901 (20130101) |
Current International
Class: |
C08F
234/00 (20060101); C08F 234/02 (20060101); H05K
1/03 (20060101); H05K 3/28 (20060101); H05K
001/00 () |
Field of
Search: |
;174/258 ;428/901
;361/397,398 |
References Cited
[Referenced By]
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Foreign Patent Documents
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2654986 |
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2813622 |
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233443 |
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DD |
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46-37972 |
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50-2256 |
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52-10554 |
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54-100477 |
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54-135400 |
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55-72025 |
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55-159975 |
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56-8321 |
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57-84403 |
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59-116701 |
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JP |
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59-155435 |
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59-195203 |
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JP |
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59-200201 |
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JP |
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60-19106 |
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JP |
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60-147703 |
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Aug 1985 |
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JP |
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60-205403 |
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Oct 1985 |
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JP |
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60-260905 |
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Dec 1985 |
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JP |
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61-20909 |
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Jan 1986 |
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JP |
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61-63802 |
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Apr 1986 |
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JP |
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61-103107 |
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May 1986 |
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JP |
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61-114208 |
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May 1986 |
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JP |
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61-179735 |
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Aug 1986 |
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JP |
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61-223806 |
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Oct 1986 |
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JP |
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61-252507 |
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Nov 1986 |
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JP |
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61-258813 |
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Nov 1986 |
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JP |
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62-47605 |
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Mar 1987 |
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JP |
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819218 |
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May 1981 |
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SU |
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Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Sarofim; N.
Attorney, Agent or Firm: Steyermark; Paul R.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a division of application Ser. No. 07,148,012 filed Dec.
28, 1989, U.S. Pat. No. 4,948,851 which is a division of
application Ser. No. 07/148,579, filed Jan. 26, 1988, abandoned
which was a divisional of application Ser. No. 904,095, filed Sept.
4, 1986, now U.S. Pat. No. 4,754,009, which was a
continuation-in-part of application Ser. No. 723,649, filed Apr.
16, 1985, now abandoned, which was a divisional of application Ser.
No. 591,486, filed Mar. 20, 1984, now U.S. Pat. No. 4,530,569,
which was a continuation-in-part of application Ser. No. 294,789,
filed Aug. 20, 1981, now abandoned.
Claims
I claim:
1. A composite substrate for the manufacture of circuit boards
manufactured from an amorphous dipolymer of 65-99 mole % of
perfluoro-2,2-dimethyl-1,3-dioxole with a complementary amount of
tetrafluoroethylene, the glass transition temperature of the
dipolymer being at least 140.degree. C.
2. An electronic current carrying component or device containing at
least one dielectric element made of an amorphous dipolymer of
65-99 mole % of perfluoro-2,2-dimethyl-1,3-dioxole with a
complementary amount of tetrafluoroethylene, the glass transition
temperature of the dipolymer being at least 140.degree. C.
3. An article of electronic circuitry having on at least one of its
exposed surfaces a protective coating of an amorphous dipolymer of
65-99 mole % of perfluoro-2,2-dimethyl-1,3-dioxole with a
complementary amount of tetrafluoroethylene, the glass transition
temperature of the dipolymer being at least 140.degree. C.
Description
BACKGROUND OF THE INVENTION
This invention relates to certain amorphous perfluoropolymers which
are particularly suitable as cladding materials in optical fiber
constructions as well as in certain electronics applications,
molded articles, and films.
While tetrafluoroethylene homopolymers and copolymers have many
excellent properties, they usually suffer from low modulus,
especially at elevated temperature; poor creep resistance;
insolubility; and in some cases intractability. Various
fluoropolymers have been proposed from time to time for cladding
optical fibers, mainly because of their low refractive indices. A
good polymeric cladding material for optical fibers should be
completely amorphous because crystallites present in polymers would
cause light scattering. Further, it should have a high glass
transition temperature, Tg, especially if intended for use at high
temperatures because above its Tg it would lose some of its
desirable physical properties and in particular it would be unable
to maintain good bonding to the fiber core. A desirable Tg would be
above 140.degree. C., preferably above 180.degree. C., especially
above 220.degree. C. Suitable, entirely amorphous fluoropolymers
having significantly high Tg's have not been heretofore
reported.
U.S. Pat. No. 3,978,030 to Resnick describes certain polymers of
perfluoro-2,2-dimethyl-1,3-dioxole (PDD), which has the following
formula: ##STR1## The above patent describes both homopolymers of
PDD, which are not further characterized, and a crystalline
copolymer with tetrafluoroethylene (TFE), which has a melting point
of about 265.degree. C.
Since Resnick's discovery of PDD homopolymer, it has been
established that the material is amorphous and has a ver high Tg of
about 330.degree. C. The homopolymer, however, is not readily
melt-processible because of poor flow and some degradation.
Crystalline copolymers of PDD with TFE cannot be used in many
applications, where, for example, optical clarity, dimensional
stability, solubility, or high Tg is required.
The polymers of U.S. Pat. No. 3,978,030 have thus not been produced
commercially, in spite of the fact that perfluoro polymers having
desirable properties would have many possible uses in various high
technology applications.
It has now been found that the dioxole PDD forms amorphous
copolymers that have unique properties that make them particularly
suitable for a number of special applications requiring high
performance.
SUMMARY OF THE INVENTION
According to this invention, there are now provided articles made
from amorphous copolymers of 65-99 mole % of
perfluoro-2,2-dimethyl-1,3-dioxole with complementary amounts of
tetrafluoroethylene, the glass transition temperature of the
copolymer being at least 140.degree. C.;
As used herein, the term "complementary" means that the mole
percentage of perfluoro-2,2-dimethyl-1,3-dioxole plus the mole
percentage of tetrafluoroethylene add together to 100%.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plot of the molar fraction of TFE in dipolymers with
PDD versus the Tg of the dipolymer.
FIG. 2 is a plot of the molar fraction of PDD in dipolymers with
TFE versus the Tg of the dipolymer.
FIG. 3 is a plot of dynamic moduli of a PDD copolymer with TFE and
a comparison resin.
DETAILED DESCRIPTION OF THE INVENTION
The copolymers useful in the present invention preferably have a Tg
of at least 180.degree. C. The especially preferred copolymers
useful in the present invention have a Tg of at least 220.degree.
C. TFE is made in large quantities by E. I. du Pont de Nemours and
Company.
The amorphous copolymers useful in the present invention, are
soluble at room temperature in perfluoro(2-butyltetrahydrofuran),
which is a commercial solvent available from 3M Company under the
tradename FC-75. In addition, they have the following outstanding
combination of properties:
1. high glass transition temperatures;
2. high moduli, especially at elevated temperatures;
3. high strengths, especially at elevated temperatures;
4. low creep under compressive load.
5. melt fabricability at moderate temperatures;
6. fabricability into films and coatings by solvent casting;
7. low temperature sprayability;
8. unusually low refractive indices;
9. excellent dielectric properties;
10. excellent chemical resistance.
The first four characteristic properties of the copolymers of the
present invention are particularly advantageous in applications
where the polymer must bear a load at an elevated temperature.
Because of their chemical inertness and excellent dielectric
properties, they also are suitable for a number of specialized
electrical applications.
Also, because of their chemical inertness, good optical properties,
and good physical properties, they are suitable for the manufacture
of optical lenses. The polymers of this invention can also be
filled or reinforced with solid substances to make composite
materials. The additives include, i.a., graphite, graphite fibers,
aramid fibers, mica, wollastonite, glass fibers, etc. Fibrous
material may be in the form of loose fibers, fabrics, or mats. Such
composite materials show enhancement of desirable properties such
as modulus, for example.
Films of the amorphous copolymers of this invention are useful when
thermally laminated to other polymeric films or metal foils. A
laminate of the amorphous copolymers of this invention with copper
foil is a superior substrate for flexible circuit production
because the copolymer bonds directly with the copper without the
necessity for an intervening adhesive. Conventional
copper/adhesive/polyimide/adhesive/copper structures for electronic
circuit substrates have the deficiency of high dielectric constant
material next to copper. This limits the ultimate speed of the
electronic circuit. A laminate of copper/amorphous copolymer/copper
permits very high circuit speeds because the amorphous copolymer
film has a low dielectric constant (2.1) and can be thermally
bonded directly to circuit copper.
A thermal laminate of amorphous copolymer/polyimide/amorphous
copolymer is useful as an electronic circuit substrate. Compared to
polyimide film itself, this laminate is a superior circuit
substrate because (a) it may be thermally bonded to copper foil
without adhesive; (b) the low water absorption of the amorphous
copolymer gives the substrate greater dimensional stability in
humid environments; and (c) the low dielectric constant of the
amorphous copolymer allows the fabrication of a high speed
circuit.
A thermal laminate of amorphous copolymer/polyimide is useful as a
vacuum bag for the curing of parts such as helicopter blades made
from carbon fiber reinforced thermoset. The high glass transition
temperature, thermal stability and low surface energy of the
amorphous copolymer give the laminate excellent release properties
when this side is placed against the thermoset part to be cured.
The polyimide layer of the laminate provides strength to prevent
pinholing when the bag enclosing the thermoset part is evacuated
and raised to curing temperature. After curing and cooling the
laminate is easily separated from the part.
A thermal laminate containing film of amorphous copolymer as its
outer faces and a film of oriented polypropylene as the core is
useful as a low-cost film structure with outstanding chemical
resistance and stain resistance combined with excellent mechanical
properties. Such laminates can be used to protect sensitive
instruments from environmental damage.
Pipe, tubing and fittings which are made from or lined with the
amorphous copolymer of this invention prevent the contamination of
the process liquid with metal ions, plasticizer, or degradation
products from the fluid handling system. Such fluid handling
components are of very high purity, are inert to most common
chemicals, and are easily fabricated by injection molding,
extrusion, machining from stock. Alternatively, fluid handling
system components may be fabricated from metal, glass, or other
plastic and subsequently lined with amorphous copolymer of this
invention by solution coating, dispersion coating, or electrostatic
powder coating. In addition to pipe, tubing and fittings, other
useful fluid handling articles made from the amorphous copolymers
of this invention are pump housings, pump impellers, valve bodies,
valve stems, valve seals, diaphragms, tanks, trays, pipettes,
laboratory vessels. Such articles are especially useful in
semiconductor processing fluid handling systems where
parts-per-billion purity is required in process water and
chemicals. Also, in molecular biology research laboratories where
extreme purity is required, and microgram quantities must be
completely released from the vessels in which they are handled, the
fluid handling articles made from the amorphous copolymer of this
invention are particularly useful.
The amorphous copolymers of this invention are particularly useful
when fabricated into articles to transport materials and components
through chemical treatment processes. For example in the
manufacturing process for semiconductor chips the silicon wafers
must be transported through a series of chemical treatment steps;
the containers in which the silicon wafers are carried must be
chemically inert to prevent contamination of the chips, and they
must be rigid and dimensionally stable to permit precise automatic
positioning at each stage of the process. Compared to the
conventional fluoroplastics used for such wafer carriers, e.g., the
copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether),
the amorphous copolymers of the present invention have greater
rigidity and greater dimensional stability. This advantage makes
possible the fabrication of larger wafer carriers, e.g, baskets to
hold silicon wafers of 30 cm in diameter; wafer carriers made from
conventional fluoroplastics are too low in flexural modulus to be
useful for wafers larger than about 15 cm in diameter.
Other conveying system components for which articles made from the
amorphous copolymers of the present invention are especially well
suited are guide rails, conveyor belt links, bearings and rollers,
clamps, racks, hooks, positioning pins, robot arm jaws and fingers,
gears, cams and similar mechanical parts which must be precisely
engineered, have good high temperature mechanical properties,
retain dimensions, be chemically pure and chemically inert.
Conveying system components made from the amorphous copolymers of
this invention exposed to corrosive chemicals or ultrapure water
are superior to all conventional fluoroplastics because of the
superior high temperature mechanical properties and dimensional
stability of the polymers of this invention.
The low dielectric constant (2.1) and low coefficient of thermal
expansion of the amorphous copolymers of this invention make them
especially useful as dielectrics in electrical and electronic
applications. For example, the dielectric used between the separate
circuit layers in high speed digital multi-layer circuit boards
must be very low in dielectric constant and be very dimensionally
stable (comparable to ceramic and copper) from -20.degree. C. up to
soldering temperature of approximately 225.degree. C. Polyimide is
dimensionally stable but has a high dielectric constant (>3); in
addition it is susceptible to atmospheric moisture; the amorphous
copolymers of this invention do not have these deficiencies, and
multilayered circuits which have this polymer as a dielectric
between circuit layers are capable of greater speed and greater
circuit density.
The low moisture absorption, outstanding chemical resistance,
purity, thermal stability, and dimensional stability of the
amorphous copolymers of this invention make them especially suited
for the protection of sensitive electronic circuits and components.
Unlike conventional fluoroplastics the polymers of the present
invention can be dissolved to form coating and encapsulating
solutions. For example, a so-called "smart connector" may be
encapsulated by dipping it, pins up, in a solution of the amorphous
copolymer of Example 1 and evaporating the FC-75 solvent to leave a
protective film of polymer to exclude environmental water and
corrosive chemicals. In another embodiment the polymers of this
invention may be used instead of a thin layer of gold, so-called
"gold flash", to protect electronic connectors from corrosion from
atmospheric chemicals. Whole electronic or electro-optic circuits
may be encapsulated by the amorphous copolymers of this invention
by a solution coating process, which is not possible with
conventional fluoropolymers because of their insolubility in
practical solvents. It is well known that aqueous dispersions of
conventional fluoropolymers may be used to impregnate and
encapsulate articles such as glass fabric and metal parts; however,
the application of such dispersions is limited to substrates which
can tolerate the high baking temperatures (>200.degree. C.)
required to fuse the fluoroplastic into a pinhole-free coating. In
contrast to aqueous dispersions of conventional fluoroplastics,
solutions of the amorphous copolymers of the present invention may
be applied to temperature sensitive substrates such as electronic
circuits or electronic components made from thermoplastics, and the
solvent evaporated at moderate temperature (100.degree. C. or less)
to leave a protective polymer film without the necessity of high
temperature baking to fuse the polymer.
As the amount of PDD in the copolymers of the present invention
increases, the Tg also increases, although not necessarily in a
linear fashion. The relationship between the mole fraction of TFE
in the dipolymer with PDD and the Tg is shown in FIG. 1. It can be
seen, for example, that a copolymer containing about 30 mole
percent TFE has a Tg of 153.degree. C., while a copolymer
containing about 23 mole % TFE has a Tg of 176.degree. C.
FIG. 2 shows the relationship between the mole fraction of PDD in
the dipolymer with TFE and the Tg. In this case, the mole fractions
of the monomers were determined by a different technique from that
used to obtain the plot of FIG. 1.
Tg is determined by differential scanning calorimetry (DSC)
according to ASTM method D-3418. Examination of the DSC curve shows
only a second order transition and no first order transition,
indicating the absence of crystallinity. The relative proportions
of the comonomers in the copolymer can be determined by fluorine-19
nuclear magnetic resonance spectroscopy (.sup.19 F NMR). This was
the technique used to obtain the plot of FIG. 1. The proportion of
hydrogen-cohtaining monomers can be determined by proton NMR
together with .sup.19 F NMR.
The proportions of comonomers in the copolymers also can be
determined by x-ray fluorescence (XRF). This was the technique used
to generate the plot of FIG. 2. Measurements were made on a Philips
Electronic Instruments 1404 XRF spectrometer. Samples were in the
form of 50 mm disks approximately 1 mm thick. Calibration of x-ray
fluoroescence intensity as a function of weight % oxygen and
fluorine was accomplished using three polymer samples of known
composition which bracketed the anticipated fluorine and oxygen
content of the unknown PDD-TFE copolymers. These standards were PDD
homopolymer, a copolymer of 40 weight % of perfluoro(methyl vinyl
ether) with 60 weight % of tetrafluoroethylene, and a copolymer of
96.1 weight % of tetrafluoroethylene with 3.9 weight % of
perfluoro(propyl vinyl ether). The compositions of the latter two
polymers were determined by infrared spectroscopy methods which had
been calibrated by accurate determination of off gases during
polymerization.
The analytical crystal used had an effective d spacing of
approximately 5.0 nm. The fluorine fluorescence intensity maximum
was at 43.5.degree. 28, and
oxygen intensity maximum at 57.1.degree. 20. Five PDD-TFE
copolymers of unknown composition spanning the composition range of
approximately 20 to 90 mole % PDD were analyzed by XRF. Ten
replicate determinations of a sample containing 63.7 wt % fluorine
and 11.2 wt % oxygen (corresponding to 71.9 mole % PDD, 28.1 mole %
TFE) gave a root mean square variance of 0.34% relative in fluorine
and 1.9% relative in oxygen.
The copolymers of PDD with TFE are readily melt-processible, so
that they can be fabricated into articles by such techniques as,
e.g., injection molding and extrusion. Furthermore, they have low
refractive indices, which is a particularly desirable feature for
optical fiber cladding. Since they are soluble in FC-75, they can
be conveniently applied to substrates, such as optical fibers or
flexible or rigid circuit boards, from solution to give thin
polymer layers. Furthermore, films of these copolymers are clear
and transparent, compared with hazy or translucent films of
crystalline polymers. For this reason, the amorphous copolymers of
the present invention are suitable for such applications as, for
example, windows for chemical reactors, especially for processes
using or manufacturing hydrogen fluoride.
It is to be noted that, while PDD homopolymers also are amorphous
and have good chemical properties, they are not readily
melt-fabricable because of some degradation occurring at the high
processing temperatures required.
Copolymerization is carried out in the presence of a free radical
generator at a temperature suitable for the initiator chosen. Well
agitated pressure equipment and a nontelogenic solvent or diluent
should be used, preferably one that has sufficient volatility to
permit easy removal from the polymer.
This invention is now illustrated by the following examples of
certain preferred embodiments thereof, where all parts,
proportions, and percentages are by weight, unless otherwise
indicated. Most Tg's were determined using Du Pont Differential
Thermal Analyzer Model 1090 with 910 or 912 DSC modules. All units
have been converted to SI units.
EXAMPLE 1
A 330 mL cold, stainless steel shaker tube was charged with 51 g
(0.21 mole) of PDD, 330 g of cold
1,1,2-trichloro-1,2,2-trifluoroethane and 0.2 g of
4,4'-bis(t-butylcyclohexyl) peroxydicarbonate. The tube was sealed,
cooled further to between -50.degree. C. and -80.degree. C. in a
dry ice-acetone mixture, alternately evacuated and flushed with
nitrogen three times, and charged with 1 g (0.01 mole) of TFE. The
tube was shaken horizontally with heating 1 hour each at 55.degree.
C., 65.degree. C. and 70.degree. C. After cooling to room
temperature, the solvent was distilled, leaving behind a solid,
white polymer, which was dried in a vacuum oven at 130.degree. C.
The monomer composition was found by NMR to be 98 mole of PDD and 2
mole % of TFE.
EXAMPLE 2
A cold 400 mL stainless steel shaker tube was charged with 270 g of
cold 1,1,2-trichloro 1,2,2-trifluoroethane, 42.2 g (0.17 mole) of
cold PDD (which had been purified in a final step by passage
through silica gel), 0.2 g of 4,4-bis(t-butylcyclohexyl)
-peroxydicarbonate; the tube was sealed and further cooled to
between -50.degree. C. and -80.degree. C. At this point the tube
was placed on a horizontal shaker, connected to the necessary
tubing and temperature sensing device. The tube was then
alternately evacuated and purged with nitrogen at least 3 times;
the evacuated tube was then charged with 2 g (0.02 mole) of
tetrafluoroethylene (TFE). Agitation, at the rate of 180 strokes
per minute, was commenced and the tube contents were heated to
55.degree. C.; after 1 hour at 55.degree. C., the temperature was
raised to 60.degree., 65.degree., 70.degree., and 75.degree. C. and
held at each of these subsequent temperatures for 1 hour. The tube
pressure was initially 124.1 kPa at 5.degree. C. and gradually
increased to 172 kPa at 75.degree. C. The tube and contents were
cooled to room temperature and the contents, a thick, white,
slurry, were discharged into a still. The solvent was distilled off
at room temperature and reduced pressure; the solid polymer was
then dried in a vacuum oven at 60.degree. C. and finally at
145.degree. C. in a circulating air oven. The dried polymer weighed
39.4 g; the Tg was 250.degree. C. and the polymer was amorphous as
evidenced by the absence of a melting endotherm; the inherent
viscosity was 0.0719 m.sup.3 /kg, determined for a 0.36% w/v
solution in perfluoro(2-butyltetrahydrofuran) at 25.degree. C.
Part of the polymer was molded at 300.degree. C. into 0.32 cm thick
by 1.3 cm wide bars which were used for the determination of
modulus vs. temperature, as shown in Table I; analysis showed it
was an 89 mole % PDD/11 mole % TFE polymer.
Another part of the polymer was compression molded at
280.degree.-300.degree. C. into 1 cm thick and 1.3 cm wide bars.
Sections of these were used in the deformation under 6.895 MPa
compressive load tests shown in Table II.
Another portion of the polymer was compression formed at
280.degree. C. into 0.027 cm thick films. These were tested for
tensile properties and reported as polymer C in Table III
COMPARATIVE EXAMPLE A
A copolymer was made from 2 parts of PDD and 10 parts of TFE
according to the exact procedure of Example 3 of U.S. Pat. No.
3,978,030 to Resnick. This polymeric product was extracted for 25
hours with 1,1,2-trichloro-1,2,2-trifluoroethane. About 0.2 percent
of the product weight was thus removed; the extracted fraction was
a grease and appeared to consist of shaker tube lubricant and a
small amount of an unknown fluorocarbon. This obviously was a low
molecular weight material. The extracted product had no Tg between
25 and 200.degree. C. It was different from the amorphous
copolymers of this invention. The solid extraction residue was a
crystalline, rather than an amorphous polymer, as shown by
wide-angle x-ray powder diffraction spectroscopy. This comparative
experiment shows that at monomer ratios employed in Example 3 of
U.S. Pat. No. 3,978,030 no amorphous PDD/TFE copolymer is
obtained.
COMPARATIVE EXAMPLE B
A mixture of 5.0 g of PDD, 0.100 g of
4,4'-bis(t-butylcyclohexyl)peroxydicarbonate, and 40.0 g of
1,1,2-trichloro-1,2,2-trifluoroethane was placed in a pressure
tube. The mixture was thoroughly degassed, sealed, and placed in a
constant temperature bath at 30.degree. C. for 20 hours. The
polymerization mixture appeared as a thick, translucent slurry of
polymer particles dispersed in
1,1,2-trichloro-1,2,2-trifluoroethane. The volatile material was
removed by distillation, and the polymer residue was dried at
150.degree. C. for 20 hours to give 4.7 g of PDD homopolymer. The
products of four identical runs were combined. The polymer had two
glass transition temperatures, at 333.degree. and 350.degree.
C.
Some physical properties of a typical PDD homopolymer are compared
with those of the 89 PDD/11 TFE dipolymer of Example 2 and those of
prior art polymers, as shown below in Tables I and II.
TABLE I ______________________________________ Young's Modulus
(GPa) of Melt Fabricated Fluorocarbon Polymers At Three
Temperatures Polymer Composition 23.degree. C. 100.degree. C.
200.degree. C. ______________________________________ PDD
Homopolymer 0.95 0.53 0.31 *98 PDD/2 TFE Copolymer 1.17 0.97 0.58
(soluble, amorphous) *89 PDD/11 TFE Copolymer 1.25 0.82 0.54
(soluble, amorphous) TFE Homopolymer (Commercial) 0.59 0.29 -- U.S.
Pat. No. 3,978,030, Example 3, 0.58 0.20 -- *94 TFE/6 PDD Copolymer
(insoluble, crystalline) ______________________________________
*Composition in mole %
It must be mentioned that PDD homopolymer could not be
melt-fabricated by compression molding without some degradation
(evidenced by gas evolution). Moldings could be obtained within the
temperature range 355.degree.-370.degree. C. Above 370.degree. C.,
the degradation was quite noticeable; below 350.degree. C., the
polymer flow was insufficient for producing moldings, and
coalescense to a homogeneous test slab was not achieved.
PDD homopolymer could be cast from
perfluoro(2-butyltetrahydrofuran) solution. That material had good
physical properties (e.g., high modulus) but this technique is
impractical for thick parts.
Polymer samples also were tested for deformation under a 1000 psi
(6.895 MPa) compressive load. The results, as measured by ASTM
D-621, are shown in Table II.
TABLE II ______________________________________ Deformation (%)
Under 6.895 MPa Compressive Load 0.5 1.0 24 Hr. Hr. Hr.
______________________________________ At 23.degree. C. TFE
Homopolymer 2.4 2.5 3.6 *Crystalline 94 TFE/6 PDD copolymer 0.11
0.11 0.32 of U.S. Pat. No. 3,978,030, Ex. 3 *89 PDD/11 TFE
Amorphous, Soluble 0.05 0.05 0.08 copolymer At 100.degree. C. TFE
Homopolymer 5.5 6.0 6.4 *Crystalline 94 TFE/6 PDD copolymer 4.2 4.4
6.4 of U.S. Pat. No. 3,978,030, Ex. 3 *89 PDD/11 TFE Amorphous,
Soluble 0.08 0.08 0.13 copolymer
______________________________________ *Composition in mole %
It can be seen that the amorphous, soluble copolymer of this
invention has a lower deformation under compressive load than
either the well-known TFE homopolymer or the crystalline PDD/TFE
copolymer reported by Resnick in US 3,977,030. The difference is
particularly remarkable at 100.degree. C.
Because of its low creep under compressive load, as compared to
commercial fluoropolymers, this copolymer is, like other copolymers
of this invention, suitable in the manufacture of gaskets,
especially for use in a corrosive atmosphere, e.g., in chemical
reactors, oil drilling equipment, automobile engines, etc.
EVALUATION OF FILMS
Films 0.025-0.05 cm thick were compression molded at
230.degree.-300.degree. C. from polymer granules at 700-7000 kPa.
One of these polymers was the amorphous 89 PPD/11 TFE copolymer of
the present invention, while the prior art crystalline copolymer
was made according to the teaching of U.S. Pat. No. 3,978,030 to
Resnick, as described in Comparative Example A herein. The physical
properties of these films are reported in the following Table III,
where it can be seen that both the modulus and the tensile strength
of the amorphous copolymer of this invention are significantly
improvfed over those of the crystalline copolymer. The amorphous
copolymer is thus stiffer and stronger.
TABLE III ______________________________________ Physical
Properties of TFE/PDD Copolymers Comp. Ex. A (Crystalline Amorphous
Copolymer) Copolymer ______________________________________ Mole %
PDD 5-7 89 Tg (.degree.C.) -- 250 Tensile Properties* (23.degree.
C., 50% RH) Modulus (MPa) 620 1191 Stress (MPa) Yield 15.9 --
Maximum 20.7 30.2 Break 20.7 30.2 Strain (%) Yield 5.5 -- Break
125.3 4.3 ______________________________________ *ASTM D1708 and
D882A: Moduli derived from stressstrain curve.
EXAMPLE 3
A. Coated Articles
A typical polymer composed of 72 mole % PDD/28 mole % TFE was
prepared in accordance with the procedure of Example 2 using an
appropriate monomer ratio. The PDD/TFE copolymer was dissolved in
perfluoro(2-butyltetrahydrofuran) (FC-75) to form a 5% solution.
Two aluminum strips (101.6 mm.times.12.7 mm.times.0.127 mm) were
washed with 1,1,2-trichloro-1,2,2-trifluoroethane to remove
residual processing oils. The aluminum strips were coated with the
PDD/TFE polymer by dipping in the solution, then evaporating the
solvent in air at room temperature for at least 10 minutes. This
dipping/drying process was repeated on the aluminum strips a total
of four times to build up a PDD/TFE polymer layer. After the last
room temperature drying cycle, the coated aluminum strips were
baked in a nitrogen purged oven at 200.degree. C. for 3 hours to
complete drying. After cooling to room temperature, one of the
coated aluminum strips was partly immersed in 6 N hydrochloric acid
at 25.degree. C. and the other was partly immersed in 5 M aqueous
potassium hydroxide solution at 25.degree. C. After immersion in
the reagents and for a period of 30 minutes afterwards, there was
no evolution of gas, no discoloration of the aluminum sample and
otherwise no apparent chemical reaction taking place.
The PDD/TFE-coated aluminum strips were removed from the acid/base
reagents. As a comparison, two similar aluminum strips, but
uncoated with PDD/TFE, were then immersed in 6 N hydrochloric acid
and 5 M aqueous potassium hydroxide solutions at 25.degree. C. A
chemical reaction began immediately in both the acid and base with
evolution of gas and discoloration of samples. The uncoated
aluminum strip in the potassium hydroxide solution reacted
vigorously for 15 minutes, at which time it was removed from the
reagent. The uncoated aluminum strip in the hydrochloric acid
reacted vigorously and was completely dissolved within 2 minutes
after immersion in the reagent.
This example demonstrates that metal articles can be coated with
the polymers of this invention and that such a coating offers
excellent resistance to corrosion of the metal substrate by
aggressive reagents such as concentrated acids and bases.
B. Fabrication of Film and Lamination to Copper Foil
A typical polymer composed of 72 mole % PDD/28 mole % TFE was
prepared in accordance with the procedure of Example 2. The polymer
was fabricated into a film by heating 5.5 g of the resin to
250.degree. C. between the platens of a hydraulic lamination press
under an applied force of 88.9 kN for 10 minutes, then cooling
rapidly to 25.degree. C. while the applied pressure was maintained.
The round film thus produced measured 140 mm in diameter and varied
between 0.14 mm and 0.19 mm in thickness. The polymer film was
laminated on both sides to rolled, annealed copper foil 25.4 m
thick by contacting the polymer film between two sheets of the
copper foil and heating the multilayered structure to 250.degree.
C. between the platens of a hydraulic lamination press under an
applied pressure of 2.07 MPa for 5 minutes, then cooling rapidly to
25.degree. C. while the applied pressure was maintained. Inspection
of the article after removal from the hydraulic press revealed a
copper-clad laminate structure, whereby the copper foil was firmly
attached to the PDD/TFE polymer film. Various properties of this
laminate structure were determined in order to evaluate its
suitability in electrical and electronics applications. The results
of these tests are given in Table IV.
This example demonstrates that metal foils can be laminated to
films fabricated from the polymers of this invention, and that
these laminates have unique properties which are highly desirable
for electrical and electronics applications.
TABLE IV ______________________________________ Test (Method)
Result ______________________________________ Dimensional
Stability: -0.72% (IPC-FC-241A method 2.2.4) 90.degree. Peel
Strength: 158 newtons/m (IPC-FC-241A method 2.4.9) Dielectric
Constant: less than 2.3 (ASTM D-1531 at 1 mhz) Dielectric Strength:
2000 Volt/mil thickness (ASTM D-149) (7.9 .times. 10.sup.7 volt/m
thickness) Volume Resistivity: 3.0 .times. 10.sup.17 ohms-cm (ASTM
D-257) (3.0 .times. 10.sup.15 ohms-m)
______________________________________
C. Fabrication of a Composite Structure
A typical polymer composed of 72 mole % PDD/28 mole % TFE was
prepared in accordance with the procedure of Example 2. The PDD/TFE
copolymer was dissolved in perfluoro(2-butyltetrahydrofuran) to
form a 5% solution. A 101.6 mm.times.101.6 mm sheet of commercially
available KEVLAR.RTM. aramid fabric was baked under nitrogen
atmosphere at 125.degree. C. for 24 hours to remove any absorbed
water vapor. After cooling to room temperature the KEVLAR.RTM.
fabric was impregnated with the PDD/TFE polymer by immersing the
fabric in a shallow pool of the PDD/TFE polymer solution using care
to exclude trapped pockets of air. The FC-75 solvent was
subsequently allowed to evaporate at room temperature, thereby
depositing the PDD/TFE polymer within the fabric in intimate
contact with the individual fibers of the fabric. The
polymer-impregnated fabric was then dried completely by baking at
200.degree. C. for 4 hours.
The resulting composite structure contained 45% by weight of
PDD/TFE resin and was a flat and stiff sheet, as compared to the
limp unimpregnated KEVLAR.RTM. fabric. This example demonstrates
that fabric materials can be impregnated with the polymers of this
invention by suitable application in solution to produce composite
structures.
EXAMPLE 4
A copolymer containing 97.2 mole % of PDD and 2.8 mole % of TFE was
prepared according to the general technique of this invention. The
copolymer had an inherent viscosity of 0.128 m.sup.3 /Kg, as
measured at 30.degree. C. in a 0.0333 Kg/L solution in FC-75, and a
Tg of 311.degree. C.
EXAMPLE 5
A PDD copolymer with TFE was prepared as follows:
A 400 mL stainless steel shaker tube was charged with 0.15 g of
4,4'-bis(t-butylcyclohexyl) peroxydicarbonate, 50.0 g (0.205 mole)
of PDD, 450 g of 1,1,2-trichloro-1,2,2-trifluoroethane, and 1.5 g
(0.015 mole) of TFE and heated at 60.degree. C. for 6 hours. The
volatile material was evaporated, and the residue was dried at
150.degree. C. for 24 hours to give 45.3 g of dipolymer. The
dipolymer had an inherent viscosity of 0.0927 m.sup.3 /Kg and a Tg
of 261.4.degree. C.
FIG. 3 is a plot of dynamic flex modulus vs. temperature of a
polymer of the same type from a different run (Tg=250.degree. C.).
This curve was obtained using a Du Pont DMA-981 Dynamic Mechanical
Analysis module with temperature controlled by a Du Pont Series 99
thermal analyzer. The heating rate was controlled at 10.degree.
C./min. The polymer sample was in the form of a small compression
molded bar. In this instrument, the sample is oscillated at its
resonant frequency, generally between 2 and 70 Hz. An amount of
energy equal to that lost by the sample is added during each cycle
to keep the sample in oscillation at constant amplitude. As the
temperature is changed, the resonant frequency also changes and is
monitored by the instrument. The Young's modulus at any temperature
is proportional to the square of resonant frequency, so that
resonant frequency data as a function of temperature can be
converted to Young's modulus as a function of temperature using an
equation, which can be found in "Instruction Manual, 981 Dynamic
Mechanical Analyzer", PN 980010-000, E.I. du Pont de Nemours &
Co., Wilmington, Delaware, 1979, rev. B.
A control plot for a commercial fluoropolymer, designated "PFA",
also was obtained.
Interpretation of Curves:
The ordinate of the plot is the dynamic modulus in Gpa. The curve
is characterized by a gently decreasing modulus as temperature
increases until the Tg of the resin is encountered (upper use
temperature), at which point the decrease in modulus becomes very
steep. The curve clearly shows the superior modulus of the PDD
dipolymer in comparison to commercial fluoropolymer. A.t all
temperatures within the working limits of the PDD dipolymer (below
the Tg), its dynamic modulus is substantially higher than that of
the commercial resin. The horizontal line at 5.5 GPa is a visual
aid. It emphasizes that at 200.degree. C., the polymer of this
invention has a modulus equivalent to that of PFA at room
temperature.
EXAMPLE 6
A dipolymer of PDD with TFE was prepared according to the general
technique described herein. It contained about 90 mole % PDD.
Thermal coefficient of expansion was determined for this sample
using a Du Pont 943 thermomechanical analyzer controlled by a Du
Pont 990 thermal analyzer. The method was similar to that described
in ASTM method E-8318-81 but was modified to test polymer samples
in tension in the form of thin films. The thermal coefficient of
expansion of the clamps used to hold the sample was determined by
measuring the apparent change in length of a standard quartz rod
clamped in the instrument over the temperature range of interest. A
standard copper sample was next measured over the same temperature
range. The actual, corrected change in length of the copper sample
was obtained as the difference between the quartz and copper data.
Since thermal coefficient of expansion of copper as a function of
temperature is accurately known, the constant relating change in
length to thermal coefficient of expansion can be calculated as a
function of temperature for the instrument.
In order to measure thermal coefficient of expansion for a polymer
sample, a thin film of the sample, generally between 0.127 and
0.381 mm thick, was mounted in the instrument, and the change in
length as a function of temperature was measured over the indicated
temperature range at a controlled rate of 10.degree. C./min. Each
sample was heated through the indicated temperature range twice,
data from the second heating being used to calculate thermal
coefficient of expansion versus temperature. For comparison,
similar measurements were made on commercial samples of Du Pont
tetrafluoroethylene copolymers with hexafluoropropylene
(TEFLON.RTM. FEP fluorocarbon resin) and with perfluoro(propyl
vinyl ether) (TEFLON.RTM. PFA fluorocarbon resin), as well as with
commercial tetrafluoroethylene homopolymer (TEFLON.RTM. TFE
fluorocarbon resin). The results are shown in Table V, below.
TABLE V ______________________________________ Thermal Coefficient
of Expansion (mm/mm/.degree.C. .times. 10.sup.-5) Copolymer Type
Th. Coeff. of Exp. Range (.degree.C.)
______________________________________ PDD/TFE 4.8 30-275 TEFLON
.RTM. PFA-500 LP 12.6 20-220 TEFLON .RTM. FEP 100 14.6 20-220
TEFLON .RTM. TFE 14.6 20-220
______________________________________
The above data show that the PDD/TFE copolymer of this invention
has a very low coefficient of thermal expansion, as compared with
commercial polymers of tetrafluoroethylene, and thus is
particularly suitable for applications where such property is
important, for example, in metal/plastic or plastic/plastic
laminates for use in flexible circuits or high speed computer
interconnects.
EXAMPLE 7
A cold 240 mL Hastelloy (TM) C shaker tube was charged with 80 g of
1,1,2-trichloro-1,2,2-trifluoroethane, 15 g (0.0615 mole) of PDD, 2
g (0.00474 mole) of EVE and 0.05g of 4,4'-bis(t -butylcyclohexyl)
peroxydicarbonate. The tube was sealed, evacuated while cold, and
was charged with 0.8 g (.+-.0.2 g) (0.008 mole) of TFE. The tube
was agitated at 40.degree. C. for 12 hours. The resulting
terpolymer was collected and dried 20 hours in a vacuum oven at
120.degree. C. resin 10.5 g (59% conversion) was obtained. This
terpolymer was amorphous and had a Tg of 162.degree. C. The
inherent viscosity of the terpolymer was 0.0734 m.sup.3 /kg, as
measured at 25.degree. C. in a 3.33 kg/m.sup.3 solution in FC-75.
The terpolymer had a composition of PDD/TFE/EVE=79.5/16.5/4.0 (mole
%) as determined by F-19 NMR spectroscopy.
* * * * *